function D = densityFunc(center,point_xy)
% center: the center of missing DOP : 1x2
% point_xy, the meshgrid of x_y plane, nx2 
    n = size(center,1); D = 0;
    if n == 1
        D = exp( - vecnorm(center-point_xy,2,2)  );
    else
        for i = 1:n
            D = D + exp( - vecnorm(center(i,:)-point_xy,2,2)  );
        end
    end
    dim = size(point_xy,1);
    
    if mod(sqrt(dim),1) == 0
        D = reshape(D,sqrt(dim),sqrt(dim));
    end
end

